The present invention is generally directed to an implantable medical device, e.g., an implantable sensor, and in particular is related to techniques for providing hermetic connections to such a device.
The present invention relates to semiconductor substrates, and more particularly to a semiconductor substrate fabricated to include hermetically-sealed electronic circuitry as well as non-hermetically-sealed electrodes thereon so as to form an implantable sensor or other implantable electronic device.
In U.S. Pat. No. 5,660,163 (hereafter the ""163 patent), there is disclosed an implantable glucose sensor which is fabricated on a ceramic substrate. Working electrodes and other elements associated with the sensor are exposed to a conductive fluid contained within a reservoir or inner sheath that covers the substrate. An outer sheath is also placed over the sensor, with a window formed over one of the working electrodes. A selected enzyme, such as glucose oxidate (GO), is placed within the window.
As disclosed in the ""163 patent, five wires or conductors are attached to the electrodes and connected to electronic circuitry, e.g., a circuit such as is shown in FIG. 3 of the ""163 patent. U.S. Pat. No. 5,660,163 is incorporated herein by reference in its entirety.
Additional features, aspects and improvements of a glucose sensor of the type disclosed in the ""163 patent are further disclosed in U.S. patent application Ser. No. 08/953,817, filed Oct. 20, 1997, now U.S. Pat. No. 6,081,736; Ser. No. 08/954,166, filed Oct. 20, 1997, now U.S. Pat. No. 6,119,028; and Ser. No. 08/928,867, filed Sep. 12, 1997, now U.S. Pat. No. 5,999,848; all of which are assigned to the same assignee as the present application and each of which is incorporated herein by reference in its entirety.
As disclosed in the referenced patents, an improved implantable sensor may be fabricated by placing the electrodes on one side of the substrate and by also placing an integrated circuit (IC) chip on the other side of the substrate, along with other needed electronic components, e.g., a capacitor(s), thereby forming a hybrid electronic circuit on the side of the substrate opposite the electrodes that is used to control or drive the sensor. The sensor senses the electrical current flowing to the electrodes, from which current the amount of oxygen near the electrodes can be determined, from which oxygen level determination, the amount of glucose to which the sensor is exposed can also be determined. Additionally, the sensor sends and receives information, data, and/or power from an external location over a two-conductor transmission line. The IC chip and other electronic components are hermetically sealed under a metal cover, the edges of which are hermetically bonded to the substrate. Electrical connection is established with the IC chip and other sealed components through stair-step vias or passageways that traverse through the substrate. Several of these types of sensors may be daisy-chained together, using just two conductors, as required. The outer sheath encircles the entire substrate, both the electronic circuit side with its metal cover and the sensor electrode side with its electrodes, saline solution reservoir and enzyme-filled window.
Disadvantageously, the sensor described in the referenced patents and patent applications is relatively thick. For many implantable applications, a thinner sensor is needed that still provides hermetic electrical connections to its internal circuitry. Hence, there remains a need for yet a smaller sensor that performs all of the same functions as the prior sensor, i.e., that provides working electrodes exposed to a saline with a selected enzyme placed over one electrode and with hermetically-sealed electronic circuitry controlling the sensor and communicating with other sensors and an external control unit. The present invention advantageously addresses these and other needs.
The present invention provides an implantable substrate sensor wherein electronic circuitry associated with the sensor, i.e., the IC chip, is formed within, or on, a suitable substrate, e.g., a CMOS substrate. A protective coating then covers the substrate, effectively forming a hermetically sealed package having the circuitry under the coating. In embodiments of the present invention, the circuitry has one or more electrically conductive pads for communicating and/or providing power to the circuitry. One or more electrical pathways provide hermetic electrical connection to the conductive pads for external connection to the sealed circuitry within the sealed package. Electrodes associated with the sensor may be selectively left uncovered by the protective coating, thereby allowing such electrodes to be exposed to body tissue and fluids when the sensor is implanted in living tissue.
In a first embodiment, the electrical pathway is a via that is made from a biocompatible material, e.g., platinum, that is made hermetic by either increasing its thickness, e.g., to at least 5 microns, or by ion beam deposition. Alternatively, the electrical pathways are formed from metal traces essentially parallel to the surface of the substrate that are connected at their first ends by first vias to conductive pads on the circuitry and with their second ends extending external to the sealed package, thus providing external electrical connection to the hermetically sealed circuitry. The metal traces are surrounded by a biocompatible insulation material, e.g., alumina, zirconia, or alloys of alumina and zirconia. Due to this combination of vias and metal traces surrounded by insulation material, the resulting electrical connection is hermetic.
In accordance with one aspect of the invention, a pair of thin substrate sensors made in accordance with the present invention, each having electronic circuitry formed on one side of the substrate may be placed back-to-back with the interconnecting and/or sensing electrodes facing outward. Such a back-to-back pair of substrate sensors advantageously allows the sensor electrodes to be positioned on the outside surfaces of the sensor pair substrates.
A hermetically sealed package suitable for implantation in living tissue comprises (1) a semiconductor substrate having a plurality of surfaces and having an integrated circuit formed on at least one of said surfaces, the integrated circuit having one or more electrically conductive pads for communicating and/or providing power to the integrated circuit, (2) one or more electrical pathways for providing electrical connection to the one or more electrically conductive pads, the pathways having first ends coupled to the one or more pads and second ends exposed for external electrical connection from the sealed package, and (3) an insulating material for encapsulating the integrated circuit and the semiconductor substrate surfaces except for selected portions of the second ends of the electrical pathways.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.